Sheet deskewing with automatically variable differential NIP force sheet driving rollers

ABSTRACT

A system of deskewing sheets moving in a process direction in a sheet path, such for a printer, by variably differentially driving the sheet in transversely spaced apart sheet driving nips formed by sheet driving rollers and mating idler rollers in response to sheet skew sensing. A variable differential nip force is applied via the respective idlers sufficient to provide a differential sheet driving velocity of a sheet in the respective sheet driving nips. The idler rollers may be mounted on a common shaft which is pivoted by a pivoting system to provide sufficiently different nip forces on the two driving rollers for a sufficient time to deskew the sheet. The sheet driving rollers may be commonly driven on a single fixed shaft by a single drive system.

Cross-reference is made to a co-pending commonly assigned U.S. application Ser. No. 10/855,451, filed May 27, 2004 by David L. Knierim et al, entitled “Print Media Registration Using Active Tracking of Idler Rotation” (Attorney Docket No. 20031544-US-NP).

Disclosed in the embodiments herein is an improved system for automatically deskewing sheets, in particular, printer print media sheets moving in a paper path. Sheet deskewing may be accomplished by creating a relative velocity differential between two laterally spaced apart sheet feeding nips to provide partial sheet rotation by a simple system of changing the relative nip force between the two nips in response to detected sheet skew in the sheet path.

Various types of print media sheet deskewing systems are known in the art. The following commonly owned patent disclosures are noted by way of some examples, and are incorporated by reference to the extent useful for background or other additional information or alternative apparatus, on so-called “TELER” or “ELER” sheet deskewing and optional additional side registration systems are U.S. Pat. No. 6,575,458 issued Jun. 10, 2003 by Lloyd A. Williams et al (U.S. Publication No. 20030020231 published Jan. 30, 2003) (Attorney Docket No. A1351); and U.S. patent application Ser. No. 10/237,362 filed Sep. 6, 2002 by Douglas K. Herrmann (U.S. Publication No. 20040046313 published Mar. 11, 2004) (Attorney Docket No. A1602). Various “ELER” systems do only skew and process direction position correction, without sheet side shift lateral registration. The latter may be done separately or not at all. The present improvement is applicable to both and is not limited to either. In either ELER or TELER systems, initial or incoming sheet skew and position may measured with a pair of lead edge sensors, and then two or more ELER or TELER drive rollers (having two independently driven, spaced apart, inboard and outboard nips) may be used to correct the skew and process direction position with an open loop control system in a known manner. Some ELER systems use one servomotor for process direction correction and another motor (e.g. a stepper motor) for the differential actuation for skew correction, as variously shown in Xerox Corp. U.S. Pat. Nos. 6,575,458 and 6,535,268 cited above. However, as shown in the cited art, there are also prior ELER systems with separate servo or stepper motors independently driving each of the two laterally spaced drive nips for process direction registration and sheet skew registration. The present improvement is also applicable to those systems.

There are other known types of sheet deskew systems, including what are now called “AGILE” systems. Some incorporated by reference examples are Xerox Corp. U.S. Pat. No. 6,173,952 B1 issued Jan. 16, 2001 to Paul N. Richards, et al (and art cited therein), U.S. Pat. No. 5,794,176 issued Aug. 11, 1998 to W. Milillo; U.S. Pat. No. 5,678,159 issued Oct. 14, 1997 to Lloyd A. Williams, et al; U.S. Pat. No. 4,971,304 issued Nov. 20, 1990 to Lofthus; U.S. Pat. No. 5,156,391 issued Oct. 20, 1992 to G. Roller; U.S. Pat. No. 5,078,384 issued Jan. 7, 1992 to S. Moore; U.S. Pat. No. 5,094,442 issued Mar. 10, 1992 to D. Kamprath, et al; U.S. Pat. No. 5,219,159 issued Jun. 15, 1993 to M. Malachowski, et al; U.S. Pat. No. 5,169,140 issued Dec. 8, 1992 to S. Wenthe; U.S. Pat. No. 5,278,624 issued Jan. 11, 1994 to D. Kamprath et al; and U.S. Pat. No. 5,697,608 issued Dec. 16, 1997 to V. Castelli, et al. Also, IBM U.S. Pat. No. 4,511,242 issued Apr. 16, 1985 to Ashbee, et al.

Various optical sheet lead edge and sheet side edge position detector sensors are known which may be utilized as initial sheet skew detection systems in such automatic sheet deskew and registration systems. Various of these are disclosed in the above incorporated references, and other references cited therein, such as the above-cited U.S. Pat. No. 5,678,159 issued Oct. 14, 1997 to Lloyd A. Williams, et al; and U.S. Pat. No. 5,697,608 to V. Castelli, et al.

A specific feature of the specific embodiment disclosed herein is to provide in a printing system with a paper path for feeding print media sheets in a process direction, said paper path having a sheet deskewing system, wherein said sheet deskewing system has a sheet skew detection system and at least two sheet deskewing nips transversely spaced apart across said paper path for variably differentially driving a print media sheet in said sheet deskewing nips to provide partial rotation of a print media sheet in said nips for sheet deskewing in response to said sheet skew detection system while said sheet is moving in said process direction; wherein said at least two deskewing nips are formed by first and second sheet driving rollers and mating first and second mating idler rollers; and wherein a variable differential nip force system provides a variable differential nip force in said nips to provide differential sheet feeding in said process direction in said nips with differential movement of said first and second idlers towards and away from sheet driving rollers in response to said sheet skew detection system to provide said partial rotation of said print media sheet in said nips for said sheet deskewing in response to said sheet skew detection system.

Further specific features disclosed in the embodiments herein, individually or in combination, include those wherein said first and second mating idler rollers are mounted on a pivotal member, and wherein said variable differential nip force system comprises a tilting drive system for tilting said pivotal member in response to said sheet skew detection system; and/or wherein said variable differential nip force system automatically reduces the nip force in one of said sheet deskewing nips relative to said other sheet deskewing nip sufficiently to allow a sheet therein to slip relative to said other sheet deskewing nip, and/or wherein said first and second sheet driving rollers are elastomeric and radially deformable, to provide a variable differential radial deformation at least one of said radially deformable sheet driving rollers; and/or wherein said variable differential nip force system automatically increases the nip force in one of said sheet deskewing nips relative to said other sheet deskewing nip to provide said variable differential driving of said sheet in said sheet deskewing nips, and/or wherein said first and second sheet driving rollers have a nominal radius and are mounted on a common drive shaft, and wherein said first and second idler rollers are non-elastomeric rollers on a common idler roller mounting shaft; and/or wherein said common idler roller mounting shaft is pivotal about a pivot axis between said first and second idler rollers; and/or wherein said variable nip force system forcibly pivots said common idler roller mounting shaft about said pivot axis in response to said sheet skew detection system to provide said partial rotation of said print media sheet in said nips for said sheet deskewing in response to said sheet skew detection system; and/or wherein a spring system maintains a nominal nip force in said sheet deskewing nips, and/or a method of deskewing sheets moving in a process direction in a sheet path with a sheet deskewing system, comprising: variably differentially driving a sheet moving in said process direction for sheet deskewing by partially rotating that sheet by variably differentially driving that sheet with at least two transversely spaced apart sheet deskewing nips, wherein said sheet deskewing nips are formed by first and second sheet driving rollers and mating first and second idler rollers, and applying a variable differential nip force to said first and second idlers in response to sheet skew detection sufficient to provide said variable differential driving of said sheet in said sheet deskewing nips sufficient to provide said partial rotation of said sheet in said nips for said sheet deskewing, and/or wherein said first and second idler rollers are automatically variably differentially driven towards and away from said first and second sheet driving rollers to change their respective nip forces; and/or said first and second sheet driving rollers are commonly driven by a common drive system on a single fixed drive shaft, and/or wherein said first and second idler rollers are commonly rotatably mounted on a pivotal mounting member which is automatically variably pivoted to oppositely move said first and second idler rollers towards and away from said first and second sheet driving rollers to change their respective nip forces; and/or wherein said first and second sheet driving rollers are elastomeric and radially deformable, and/or wherein said applying of said variable differential nip force to said first and second idlers is in response to sheet skew detection by forcibly pivoting said common idler roller mounting shaft about said pivot axis in response to said sheet skew detection to provide said variable differential driving of said sheet, and/or wherein said first and second idler rollers are rotatably mounted on a common idler roller mounting member pivotable about a pivot axis intermediate of said first and second sheet driving rollers; and/or wherein said variable differential nip force is provided by forcibly pivoting said mounting member about said pivot axis from adjacent to one end thereof.

The disclosed system may be operated and controlled by appropriate operation of conventional control systems. It is well known and preferable to program and execute imaging, printing, paper handling, and other control functions and logic with software instructions for conventional or general purpose microprocessors, as taught by numerous prior patents and commercial products. Such programming or software may, of course, vary depending on the particular functions, software type, and microprocessor or other computer system utilized, but will be available to, or readily programmable without undue experimentation from, functional descriptions, such as those provided herein, and/or prior knowledge of functions which are conventional, together with general knowledge in the software or computer arts. Alternatively, the disclosed control system or method may be implemented partially or fully in hardware, using standard logic circuits or single chip VLSI designs.

The term “reproduction apparatus” or “printer” as used herein broadly encompasses various printers, copiers or multifunction machines or systems, xerographic or otherwise, unless otherwise defined in a claim. The term “sheet” herein refers to a usually flimsy physical sheet of paper, plastic, or other suitable physical substrate for images, whether precut or web fed.

As to specific components of the disclosed apparatus or methods, or alternatives therefor, it will be appreciated that, as is normally the case, some such components are known per se in other apparatus or applications, which may be additionally or alternatively used herein, including those from art cited herein. For example, it will be appreciated by respective engineers and others that many of the particular component mountings, component actuations, or component drive systems illustrated herein are merely exemplary, and that the same novel motions and functions can be provided by many other known or readily available alternatives. All cited references, and their references, are incorporated by reference herein where appropriate for teachings of additional or alternative details, features, and/or technical background. What is well known to those skilled in the art need not be described herein.

Various of the above-mentioned and further features and advantages will be apparent to those skilled in the art from the specific apparatus and its operation or methods described in the embodiment example below, including the drawing figures (which are approximately to scale) wherein:

FIG. 1 is a schematic plan view transverse an exemplary paper path of one example of a subject sheet deskewing system,

FIG. 2 is a reduced size top view thereof,

FIG. 3 is an enlarged side view of one of the sheet feeding nip sets of the embodiment of FIGS. 1 and 2, and

FIG. 4 is the same as FIG. 3 but showing an alternative embodiment in which the nip force compression of one nip provides a resultant effective drive radius change of an elastomeric drive roller of that sheet feeding nip set.

Describing now in further detail the exemplary embodiments with reference to the Figures, there is shown by way of one example a deskewing system 10 for print media sheets 12 moving in an otherwise conventional paper path of a printer or a printer output to a finisher, which thus need not be illustrated in further detail herein. The deskewing system 10 may be controlled by a conventional programmed controller 100, with, as shown in FIG. 2, initial sheet skew information conventionally detected by a skew detector system, which may be a transversely spaced pair of optical sheet lead edge detectors 102A and 102B and may include a side multi-detector array 104, as described or cited in above-cited references.

Illustrated here is a system and method of deskewing sheets based on the principle of creating a relative sheet driving velocity differential between inboard and outboard nip sets formed by idler 14 and its mating drive roller 32 on one side of the sheet path, and idler 16 and its mating drive roller 34 on the other side.

Here, the desired sheet driving velocity differential for deskewing sheet 12 in those two nips is providing by selectively changing the nip load or normal force between the two nip sets. In one embodiment, this allows limited slip in the forward sheet feeding of one nip relative to the other nip, due to normal upsteam drag forces on the sheet, which allows partial sheet 12 rotation, to accomplish desired sheet deskew. To express it in other words, the difference in drive velocity between the two laterally spaced drive nips is provided by providing a difference in coefficient of friction or drive grip between one idler and drive roller nip and the other, so that, selectively, one nip is pulling the sheet faster than the other.

In another embodiment, this selective differential between the nip loads or normal forces between the two nip sets causes small differences in the effective drive radius of elastomeric drive roller 32 and/or 34 relative to one another, as exaggerated for illustration in FIG. 4 with the difference between R1 and R2. (This alternative embodiment will rotate the sheet in the opposite direction.)

In both embodiments this may be accomplished through a simple mechanism such as that illustrated in FIGS. 1 and 2 which loads or unloads the two respective nips to create a force imbalance at the nip of one drive roller relative to the other. As shown in FIG. 1, that mechanism can be a motor M1 screw-driving a tilt mechanism 26 connected to one end of a member 17 which is pivotal about a pivot axis 20 intermediately between the two nips. The two non-elastomeric idler rollers 14 and 16 are mounted on the shaft 18 to pivot therewith and thereby change their respective nip force applying engagements with the drive rollers 32 and 34. Springs 22 and 24 or the like can apply a normal or nominal nip force, and a minimum nip force even with the shaft 18 pivoting. The normal force in both drive nips may of course be maintained above the level at which uncontrolled sheet 12 driving slip of the less-loaded drive nip could occur.

FIG. 1 illustrates exemplary positions of the springs 22 and 24. As shown, these springs 22 and 24 may be installed on an elongated pivotable support 17 and extend between that support 17 and the underlying parallel idler shaft 18. The idler shaft 18 does not need to significantly pivot. Thus, the springs can transmit the applied nip force for each idler roller 14 and 16 in proportion to the angle of tilting of the support 17 by the motor M1 via the rack drive 26. The motor M1 may be mounted on the same frame as the pivot axis 20. Therefore, even if one were to remove the effect of the spring 22 and/or spring 24, the pivotal support 17 would still retain its tilt position, because motor M1 here effectively holds one end of the support 17 and the pivot axis 20 holds the center of the support 17. That is, the embodiment of FIG. 1 shows the pivot axis 20 on a different shaft or other support 17 than the idlers, and allows the springs attached to the support 17 to transmit the nip force to the idlers. Angular tilt of the support 17 will result in one spring being more compressed and the other spring less compressed. This will create a different force on their respective idlers. When the driver rollers 32 and 34 turn, one side of the sheet 12 will be positively and more strongly gripped and the other nip may be allowed to slightly slip (in a grip/slip system embodiment). The different nip forces will produce a difference of sheet velocity between the inboard and outboard sides of the sheet 12. As noted, the amount of deskewing may be controlled by a feedback system which may be monitored by array sensor.

A completely open nip on one side (which could allow unintended gross sheet skew) may be avoided by maintaining a minimum force on the lowest nip force idler to keep control of the sheet 12, even if the sheet 12 needs to slip somewhat in a controlled manner under the low force idler. With the tilting of the support 17, when a minimum nip force is applied on one idler a maximum nip force is being applied to the other idler, thus feeding the sheet with approximately the same total nip force.

Any upstream sheet nips may, of course, be conventionally released during the deskewing operation to allow the sheet 12 to partially rotate for deskewing. The desired amount of applied deskewing (angled sheet driving) may be estimated by the controller 100 from the sensing of the initial sheet skew and the known responsive parameters of the deskewing system. For example, with a look-up table in the controller 100 derived from experimental testing of the ratio of the respective applied roller normal nip force (roller deformation force) to the corresponding drive roll radius reduction and/or increase of the two drive rollers (which corresponds to their differential sheet drive).

The system may optionally, alternatively or additionally use an additional sensor and a closed loop control system to continuously measure and feed back the change in skew during deskewing. For example, pending U.S. application Ser. No. 10/855,451 (Attorney Docket No. 20031544-US-NP), cross-referenced above on tracking idler rotation during deskewing for improved deskew accuracy could readily be incorporated by reference in combination with the subject low cost deskew system.

Once the sheet is moving straight (deskewed), the system can return the nip loading to a balanced system with equal drive roller radii. Also, any previously opened fixed nips upstream and/or downstream may re-engage. It may be seen that this system is simpler and has a lower UMC cost as compared to TELER and other deskew systems that require independent servo motors or differential drive mechanisms for the inboard and outboard nips to steer the sheet. This system may be particularly advantageous in applications for coarse sheet orientation correction before hole punching or other finishing functions.

In the alternative embodiment, a variable compression (with variable nip normal force) may be readily made via variable idler 14, 16 forces against laterally spaced commonly driven elastomeric drive rollers 32 and 34. But the drive rollers 32 and 34 themselves may still be mounted on a single common fixed shaft 30 driven by a single drive motor M2, unlike the more complex and costly cited prior art systems, yet provide differentially driven laterally spaced drive rollers by providing differential drive roller radii. It is believed that only about 3 mm of radius deformation difference between the two drive rollers can provide significant skew correction of standard sheet sizes.

It will also be appreciated that the idler roller and drive roller positions may be easily vertically reversed. If sheet process direction registration correction is not additionally required, the motor M2 could even be a constant speed motor or other drive rather than a servo or stepper motor.

Either system may be used with various sheet lead edge skew detectors and feedback systems, to provide for at least gross deskew, at much lower cost, than other cited deskew systems. Even if not as accurate for image transfer sheet registration systems, it may be suitable for finisher compilers, etc. It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Also that various presently unforeseen or unanticipated alternatives, modifications, variations or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims. 

1. In a printing system with a paper path for feeding print media sheets in a process direction, said paper path having a sheet deskewing system, wherein said sheet deskewing system has a sheet skew detection system and at least two sheet deskewing nips transversely spaced apart across said paper path for variably differentially driving a print media sheet in said sheet deskewing nips to provide partial rotation of a print media sheet in said nips for sheet deskewing in response to said sheet skew detection system while said sheet is moving in said process direction; wherein said at least two deskewing nips are formed by first and second sheet driving rollers and mating first and second mating idler rollers; and wherein a variable differential nip force system provides a variable differential nip force in said nips to provide differential sheet feeding in said process direction in said nips with differential movement of said first and second idlers towards and away from sheet driving rollers in response to said sheet skew detection system to provide said partial rotation of said print media sheet in said nips for said sheet deskewing in response to said sheet skew detection system.
 2. The printing system of claim 1, wherein said first and second mating idler rollers are mounted on a pivotal member, and wherein said variable differential nip force system comprises a tilting drive system for tilting said pivotal member in response to said sheet skew detection system.
 3. The printing system of claim 1, wherein said variable differential nip force system automatically reduces the nip force in one of said sheet deskewing nips relative to said other sheet deskewing nip sufficiently to allow a sheet therein to slip relative to said other sheet deskewing nip.
 4. The printing system of claim 1, wherein said first and second sheet driving rollers are elastomeric and radially deformable, to provide a variable differential radial deformation of at least one of said radially deformable sheet driving rollers and wherein said variable differential nip force system automatically increases the nip force in one of said sheet deskewing nips relative to said other sheet deskewing nip to provide said variable differential driving of said sheet in said sheet deskewing nips.
 5. The printing system of claim 1, wherein said first and second sheet driving rollers are elastomeric and radially deformable and have nominal radius mounted on a common drive shaft, and wherein said first and second idler rollers are non-elastomeric rollers on a common idler roller mounting shaft, and wherein said common idler roller mounting shaft is pivotal about a pivot axis between said first and second idler rollers, and wherein said variable nip force system forcibly pivots said common idler roller mounting shaft about said pivot axis in response to said sheet skew detection system to provide a variable radial deformation of a nominal radius of at least one of said radially deformable sheet driving rollers to provide said variable differential driving of said print media sheet in said sheet deskewing nips to provide said partial rotation of said print media sheet in said nips for said sheet deskewing in response to said sheet skew detection system.
 6. The printing system of claim 1, wherein said first and second idler rollers are non-elastomeric rollers rotatably mounted on a pivotal common idler roller mounting shaft which is pivotal intermediately of said nips, and wherein said variable nip force system forcibly pivots said common idler roller mounting shaft.
 7. The printing system of claim 1, wherein a spring system maintains a nominal nip force in said sheet deskewing nips.
 8. A method of deskewing sheets moving in a process direction in a sheet path with a sheet deskewing system, comprising: variably differentially driving a sheet moving in said process direction for sheet deskewing by partially rotating that sheet by variably differentially driving that sheet with at least two transversely spaced apart sheet deskewing nips, wherein said sheet deskewing nips are formed by first and second sheet driving rollers and mating first and second idler rollers, by applying a variable differential nip force to said first and second idlers in response to sheet skew detection sufficient to provide said variable differential driving of said sheet in said sheet deskewing nips sufficient to provide said partial rotation of said sheet in said nips for said sheet deskewing.
 9. The method of deskewing sheets of claim 8, wherein said first and second idler rollers are automatically variably differentially driven towards and away from said first and second sheet driving rollers to change their respective nip forces, and said first and second sheet driving rollers are commonly driven by a common drive system on a single fixed drive shaft.
 10. The method of deskewing sheets of claim 8, wherein said first and second idler rollers are commonly rotatably mounted on a pivotal mounting member which is automatically variably pivoted to oppositely move said first and second idler rollers towards and away from said first and second sheet driving rollers to change their respective nip forces.
 11. The method of deskewing sheets of claim 8, wherein said first and second sheet driving rollers are elastomeric and radially deformable.
 12. The method of deskewing sheets of claim 8, wherein said first and second idler rollers are non-elastomeric rollers on a common idler roller mounting shaft, and wherein said common idler roller mounting shaft is pivotal about a pivot axis between said first and second idler rollers, and wherein said applying of said variable differential nip force to said first and second idlers is in response to sheet skew detection by forcibly pivoting said common idler roller mounting shaft about said pivot axis in response to said sheet skew detection to provide said variable differential driving of said sheet.
 13. The method of deskewing sheets of claim 8, wherein said first and second idler rollers are rotatably mounted on a common idler roller mounting member pivotable about a pivot axis intermediate of said first and second sheet driving rollers, wherein said variable differential nip force is provided by forcibly pivoting said mounting member about said pivot axis from adjacent to one end thereof. 